The present invention relates to the conveyor art and, more particularly, to an improved split sprocket assembly, a related apparatus, and a related method of mounting a sprocket to a rotatable structure, such as a drum or shaft.
Today, in many modern manufacturing facilities, modular conveyor systems are extensively utilized to transport articles to and from various work stations during all stages of production. In recent years, manufacturers using production lines with conveyors as an integral component of the material handling system have realized reasonably significant gains in productivity and resource utilization. As a result, modular conveyor systems have become even more widely implemented and have been adapted to meet an even wider scope of the material handling needs of producers of a multitude of consumer and industrial goods. Therefore, the continual development of improved modular conveyors is necessary in order to keep pace with the demands and expectations of the users of such conveyors.
Conventional conveyor systems employing endless, modular link or roller chain belts are typically driven at one end of an elongated guide structure, such as a rail or the like supported above the ground by a frame. The driving force is transmitted from a motive device, such as a variable speed electric motor, to a plurality of gang-driven sprockets coupled to a rotating drive structure, such as a shaft or drum. At the opposite end of the guide structure, idler sprockets are coupled to a freely-rotating idler shaft or drum. As should be appreciated, the drive and idler sprockets assist in supporting and guiding the endless belt as it makes the transition from the forward run to the return run, or vice versa, at each respective end of the guide structure.
Of course, both the drive and idler sprockets are subject to wear as a result of the substantially continuous engagement maintained with the conveyor belt. If not kept in check, this wear may affect the overall performance of the conveyor system. For example, worn sprockets may allow the belt to slip, which creates both timing and efficiency problems. Hence, it is necessary to perform an inspection of the sprocket(s) from time to time to determine whether some form of ameliorative action, such as a repair operation or perhaps even a complete replacement, is required.
While inspection may only require removing the belt to gain visual access to the sprocket, repairing or completely replacing a unitary sprocket requires removing it from the corresponding support shaft or drum altogether. In the case where a single drive or idler sprocket is carried on the shaft or drum, removing the belt and the sprocket is a relatively uncomplicated undertaking. However, in the situation where a plurality of sprockets are gang driven or carried on a single support shaft or drum, removing any of the inner sprockets becomes a time and labor intensive process, since all adjacent outer sprockets and any other corresponding structures (side plates, chain guides/strippers, conveyor frame components or other support structures, etc.) must first be removed. As should be appreciated, removing even one of the sprockets in a gang-driven arrangement significantly increases the time and labor involved. Additionally, the wholesale removal and replacement of multiple sprockets carried on a shaft may create alignment and/or timing problems that must be corrected to ensure efficient operation. Of course, the time and labor required to remedy these problems further exacerbates the situation.
Others in the past have proposed a number of different types of arrangements to solve these problems. One popular proposal is to use a split sprocket consisting of two mating halves that are coupled together over a shaft. With this arrangement, removal of the sprocket can be accomplished without dismantling the entire conveyor assembly. Modem examples of various types of split sprockets are found in U.S. Pat. No. 6,202,834 to Layne et al, U.S. Pat. No. 6,146,299 to Harvey, and U.S. Pat. No. 6,086,495 to Stebnicki et al., the disclosures of which are hereby incorporated by reference.
In the case of a rotatable drive or idler drum, it is known to couple a single-piece, unitary sprocket to the drum using a plurality of cylindrical keys or pins. For example, U.S. Pat. No. 5,934,447 to Kanaris discloses an arrangement in which the drum includes a plurality of shallow grooves extending axially along its entire surface. Keys received in the sprocket fit in the corresponding shallow grooves and, as a result, keep it spaced from the outer surface of the drum. A radially extending set screw is used to press each key into the corresponding groove to rotatably couple the sprocket to the drum.
While this arrangement does provide the limited advantage of allowing for the adjustment of the position of the sprocket along the drum, there are countervailing disadvantages. For example, during extended periods of use, the set-screws may loosen and allow the keys and, hence, the sprocket to xe2x80x9cwalkxe2x80x9d or travel axially along the surface of the drum. This is deleterious, since it not only increases the wear on the sprocket, but also causes chattering and wear on the belt. If the set-screws loosen to a sufficient degree to allow the key to move out of the shallow groove in the drum, the sprocket may slip and, in the case of a driven drum, transmit no drive power or torque to the belt. Of course, the set-screws may be frequently inspected or tightened down in an effort to prevent these deleterious occurrences, but this inevitably increases the maintenance effort and overall operational cost.
Accordingly, the foregoing discussion identifies a particular need for an improved manner of mounting a sprocket to a rotatable structure, such as a drive or idler drum in a conveyor system. It is envisioned that by splitting the sprocket into two or more sections or segments, it would be possible to provide a key for each section or segment that corresponds to a separate keyway formed in the outer surface of the rotatable structure. The sections or segments could also be coupled together and held in tension, such as by tangentially-extending fasteners. The tension would create a sufficient radially-directed holding force to ensure that the keys remain securely held in the keyways during rotation while eliminating the need for radially-extending set-screws. One or more of the keyways could also be truncated and the keys sized for fitting in the truncated keyway(s) in relatively tight seated engagement. This would prevent the sprocket from traveling or xe2x80x9cwalkingxe2x80x9d along the surface of the drum in use. Overall, this combination of features would result in a sprocket assembly that is a significant improvement over those proposed in the past, especially in terms of maintenance cost, operational efficiency, and reliability.
In accordance with a first aspect of the invention, a sprocket assembly intended for mounting on a rotatable structure, such as a drum or shaft, for engaging an endless conveyor belt making the transition between a forward and a return run or vice-versa is disclosed. The assembly comprises at least three unitary sprocket sections or segments, with each of the sections or segments including an arcuate inner surface for engaging an outer surface of the rotatable structure. A plurality of fasteners are also provided, each for fastening one of the plurality of sprocket sections to an adjacent sprocket section to form the sprocket assembly.
Each of the arcuate sprocket sections or segments includes a first end and a second end. In one embodiment, the first end includes a tangentially-extending bore and the second end includes a corresponding aperture for receiving a threaded bolt forming a part of one of the fasteners. The engagement of the bolt extending through the aperture in the first end of one sprocket section or segment into the bore in a second end of the adjacent sprocket section or segment assists in securing the two structures together. In another embodiment, each of the ends includes a mating face having a matching aperture formed therein for receiving a threaded bolt forming a part of one of the fasteners. When the ends of two adjacent sprocket sections or segments are abutting in the mated position, the apertures are positioned such that a centerline extending through them is generally parallel to a line drawn tangent to a point located at an interface between the adjacent ends. To complete the fastener and secure the adjacent sections or segments together, a nut is then placed on the bolt and tightened.
Each of the sections or segments may include a receiver, or alternatively two adjacent sections or segments may together form a receiver. Each receiver is capable of receiving and holding a key that is adapted to fit into a keyway formed in or on the rotatable structure, such as a shaft or drum. The key is preferably cylindrical, in which case, the receiver is C-shaped. However, using keys having other shapes is entirely possible, with the corresponding receiver and keyway generally having a matching shape.
Instead of the three sections or segments described above, the sprocket assembly may comprise at least four sprocket sections or segments. As with the three piece embodiment, each of the four sprocket sections or segments may include a first end and a second end. Preferably, each end includes an aperture for receiving a threaded bolt forming a part of one of the plurality of fasteners. When the ends of two sprocket sections or segments are positioned adjacent to each other in abutment, a centerline extending through the matching apertures is generally parallel to a line drawn tangent to a point at an interface between the adjacent ends. To complete the assembly of the two adjacent sections or segments, a nut may be placed on the bolt and tightened.
In accordance with a second aspect of the invention, a sprocket assembly intended for mounting on the outer surface of a rotatable structure, such as a drum or shaft, for engaging an endless conveyor belt making the transition between a forward and a return run is provided. The assembly comprises a plurality of sprocket sections or segments (preferably two, three, or four), with each section or segment having an arcuate inner surface and at least two ends. Each of the ends includes an aperture and a plurality of fasteners for fastening a first end of one of the plurality of sprocket sections to a second, corresponding end of an adjacent sprocket section are provided. Specifically, the fasteners include a threaded bolt for positioning through a matching pair of the apertures in the first and second ends and a nut for placement on a portion of the bolt projecting through one of the apertures. A centerline extending through the matching pair of the apertures is generally parallel to a line drawn tangent to a point at an interface between the ends of two adjacent sprocket sections or segments when positioned in an abutting relationship. As a result of this fastening arrangement, tightening of the nut against a surface of the sprocket section or segment adjacent to the aperture through which the bolt projects creates a tension between the adjacent sprocket sections. Each sprocket section or segment may further include a C-shaped receiver for receiving a substantially cylindrical key, whereby a portion of the key projects from the inner surface of the section or segment for engaging a keyway formed in the rotatable structure and is held in place by the tension mounting.
In accordance with a third aspect of the invention, an apparatus intended for use in engaging and guiding an endless conveyor belt making the transition between a forward and a return run or vice-versa is disclosed. The apparatus comprises a structure, such as a drum or shaft, mounted for rotation about an axis. The rotatable structure includes an outer surface having a first plurality of keyways, with at least one of the first keyways being truncated and thus extending only partially across the outer surface in an axial direction. A first split sprocket comprised of at least three sections or segments is also provided. The first sprocket includes an inner surface and a plurality of receivers. A first plurality of keys are also provided, with each key being positioned at least partially in one of the receivers such that a portion thereof projects inwardly and is adapted for seating engagement in one of the first keyways. A fastener for fastening each sprocket section or segment to an adjacent sprocket section or segment is also provided.
In one embodiment, the rotatable drum is cylindrical and the inner surface of each the sprocket section or segment is arcuate. Additionally, each receiver is substantially C-shaped, in which case each key is cylindrical and is slidably received in the corresponding receiver. The corresponding keyway is also semi-circular. Instead of being slidably received, each key may be received in the corresponding receiver in snap-fit engagement. Preferably, the width of each keyway in the axial direction is substantially identical to the width of the key and the length of each keyway at the surface of the rotatable structure is substantially equal to of less than the diameter of the key.
In addition, the split sprocket may be formed of four sections or segments. The fourth sprocket section or segment is secured to one of the at least two sprocket sections or segments and the third section or segment using fasteners. Also, the fourth sprocket section or segment may include a receiver for slidably receiving a key for engaging one of the first keyways.
In addition to the first keyways, a second plurality of keyways may be provided, with at least one of the second keyways extending only partially across the outer surface of the rotatable structure in the axial direction. The apparatus may further comprise a second split sprocket comprised of at least two sections or segments having an inner surface and a plurality of receivers; a second plurality of keys, each key positioned at least partially in one of the receivers such that a portion thereof projects inwardly from the second split sprocket, the portion being adapted for seating engagement in one of the second plurality of keyways; and a second plurality of fasteners for fastening the at least two sections or segments of the second split sprocket together. A third plurality of keyways, including at least one third keyway extending only partially across the outer surface of the drum or shaft in the axial direction, may also be provided. The first or second split sprockets may be alternately fastened to the rotatable structure using the third keyways.
In accordance with a fourth aspect of the invention, a method of mounting a split sprocket over a rotatable structure, such as a drum or shaft, is provided. The method comprises fastening at least three unitary toothed sections or segments together over the rotatable structure to form a first sprocket, while simultaneously securing the sprocket to the rotatable structure so as to prevent axial movement along the outer surface thereof. The step of fastening may include securing a tangentially-extending fastener between adjacent sprocket sections or segments. The rotatable structure may include a plurality of circumferentially-aligned, truncated keyways, and the step of securing the sprocket to the rotatable structure may include positioning a key in each one of a plurality of receivers formed in the sprocket such that at least a portion of the key projects inwardly therefrom and is received in one of the keyways.